In these latter days, a MPLS (Multiprotocol Label Switching) has been used as a data-carrying mechanism that allows, by incorporating a label switching concept into an IP network, more high-speed and flexible routing than conventional IP routing that is performed using an IP address. For example, the related technology is disclosed in Japanese Laid-open Patent Publication No. 2007-235579.
In the conventional IP routing, a Hop-by-Hop method is employed in which a destination to which a data packet is transferred is determined by comparing a destination IP address of the data packet received by each node, with each of entries of a routing table held in the each node. According to this method, processing load of each node may become high, thereby causing bottleneck in packet transfer performance. Further, traffic congestion in a network may occur since processing for route selection is performed on all the data packets passing through the each node.
In a MPLS, for example, a short fixed-length identifier (for example, 20 bits in length) called a label is used instead of an IP address, and each of nodes (routers) determines a route to which a packet is to be transferred, based on the label. Further, the each of nodes stores transfer information in which each of label values is associated with one of destination addresses so that the each node determines a destination address to which a packet having the corresponding label value is to be transferred, based on the transfer information. In this way, a communication path passing through a given route is established by beforehand setting transfer information for each of nodes (routers) positioned along a communication path. Recently, a service in which a communication path is being established between required points for a required time period according to a request from an end user has been under consideration, so as to make the best use of the feature of MPLS that allows dynamically establishing a communication path passing through an arbitrary given route.
In a MPLS, when registering transfer information in each node, label information is exchanged between adjacent nodes, based on a signaling protocol such as an RSVP (Resource reSerVation Protocol). According to an RSVP, for example, a LSP (Label Switch Path) is established, triggered by a request from an origination node positioned at an end of the LSP to be established, using an on-demand ordered LSP controlling method in which a label value is sequentially assigned to a data link connecting each pair of adjacent nodes along the LSP in the direction from a termination node positioned at the other end of the LSP toward the origination node.
However, according to the above mentioned related arts, there exists a problem that it takes time to establish a communication path. For example, in an RSVP, label assignment processing is sequentially performed on a node after the node has received assignment notification (for example, a RESV message) from a adjacent downstream node that is defined as an adjacent node in the downstream direction from the origination node toward the termination node along the communication path. For this reason, a processing time required for distributing labels and establishing a communication path is linearly increases in proportion to the number of nodes passed by the communication path passes (a hop count).
In recent years, a hop count needed for transferring a data packet in a network has been increased with increasing scale of the network, thereby increasing a processing time required for establishing a communication path. Meanwhile, in a field where real-time performance is required, such as a TV broadcast system, introduction of MPLS technology allowing transmission of large volume of data has been promoted, and speeding-up of path establishment has been required.